Men are understudied in the area of sexual risk and maternal-child health. The role men play in the health and sexual decisions of young couples transitioning to parenthood has not been fully explored. The inclusion of men in prevention research is essential to understanding the interpersonal context in which decisions are made about sexual behavior, personal health, and family functioning. In the proposed research, using the guiding framework of attachment theory we will examine HIV/STI risk behavior, relationship quality, and parenting functioning for young expectant fathers and their pregnant adolescent partners from pregnancy to parenthood. Since much of sexual risk occurs in the context of romantic relationships, it is essential to understand how each member of a romantic dyad influence sexual risk behavior, and how changes in relationships during important life transitions (e.g. parenthood) influence behavioral and biological outcomes associated with HIV/STD risk. We will examine these issues in a multi- site longitudinal study of young expectant fathers and their pregnant adolescent partners (n=300 dyads) to be conducted in health clinics in Connecticut. Data will be collected through Audio Computer Assisted Self- Interview (ACASI) and semi-annual STD testing. Both members of the dyad will be assessed at three time points regardless of relationship status: during 3rd trimester of pregnancy, 6-months postpartum, and 12 months postpartum. Therefore, we can assess sexual risk behavior within couples and across new partnerships for both young men and women. The results of this study can promote theoretical development and provide empirical information to enhance current and future interventions to prevent HIV, and other STDs for both young men and women. In addition, results will inform couple-based interventions that focus on relationship maintenance and family strengthening as well as HIV prevention during times of stress and transition.